Solar battery cell and production method thereof

ABSTRACT

A method for producing a solar battery cell, includes: a first step of forming an insulating film on one face side of a semiconductor substrate; a second step of forming an electrode forming groove in an electrode forming region on the insulating film; a third step of printing an electrode printing paste including metal particles as a main component to a width that covers the electrode forming groove and a region sandwiching the electrode forming groove on the insulating film and that is wider than a width of the electrode forming groove, and then drying the electrode printing paste; and a fourth step of forming an electrode with the width of the electrode forming groove by firing the electrode paste at a temperature that is equal to or higher than a melting point of the metal particles or that is equal to or higher than a eutectic temperature, and accumulating and solidifying the electrode paste on the electrode forming groove.

FIELD

The present invention relates to a solar battery cell and a productionmethod thereof.

BACKGROUND

Conventionally, in a production process aiming to mass produce solarbattery cells having silicon (Si) as a main component, typically, apaste containing metal particles is printed on a solar battery substrateby a screen printing method, and then the paste is dried and sintered toform an electrode on the solar battery substrate (see, for example,Patent Literature 1). To improve the photoelectric conversion efficiencyof a light-receiving face side electrode provided on a light-receivingface (front face) of the solar battery cell, it is important to, whilemaintaining a low electrode resistance, reduce the electrode surfacearea on the light-receiving face, which is a factor in reducing theeffective light-receiving surface area. More specifically, it ispreferred that the light-receiving face side electrode have as high anaspect ratio (electrode thickness/electrode width) as possible whilemaintaining a low electrode resistance.

CITATION LIST

-   Patent Literature 1: Japanese Patent Application Laid-Open No.    H2-298078

SUMMARY Technical Problem

However, when a light-receiving face side electrode is formed using anormal screen printing method, the post-sintering electrode dimensionsare limited to about a width of 100 μm, a thickness of 20 μm, and anaspect ratio (electrode thickness/electrode width) of 0.2. It isdifficult to print so that the electrode has a thickness that issufficient to maintain the electrode cross-sectional area, specifically,to achieve a high aspect ratio, while further reducing the electrodewidth.

To suppress a deterioration in properties due to carrier recombinationon the back side of the solar battery cell, a lot of research is beingcarried out into structures in which an aluminum (Al) electrode is notallowed to be in direct contact with the silicon substrate, aninsulating film is formed on the back of the silicon substrate tomaintain the high-quality crystal properties of the back of the siliconsubstrate, and a back side electrode is provided by forming holes andgrooves on the insulating film. In such a structure, how finely theholes and grooves can be formed is the key point. Similar to theformation of the above-described light-receiving face side electrode,there is a need for research into methods for producing a low-resistanceprinted electrode that has a high aspect ratio.

In addition, when forming a solar battery cell electrode using a screenprinting method, a metal particle-containing paste is printed, dried,and then sintered. Therefore, the voids that were present among themetal particles in the paste after drying, remain after the sintering,and are ultimately still present in the electrode. If there are voids inthe electrode, moisture and the like, which cause the life of the solarbattery cell to deteriorate, tends to penetrate into the electrode.Consequently, in electrode formation, it is important to eliminate voidsin the electrode in order to improve the durability of the solar batterycell. Moreover, voids in the electrode are also a factor in increasingthe electrode resistance.

Therefore, when forming a solar battery cell electrode using a screenprinting method suited to low-cost mass production, it is desirable toachieve a finer electrode by improving the aspect ratio whilemaintaining a low electrode resistance, and prevent a deterioration inthe life of the solar battery cell by reducing the voids in theelectrode.

In view of the above-described circumstances, it is an object of thepresent invention to obtain a solar battery cell that can be massproduced inexpensively and has excellent photoelectric conversionefficiency and durability, and a production method thereof.

Solution to Problem

In order to solve the above problem and in order to attain the aboveobject, a method for producing a solar battery cell of the presentinvention, includes: a first step of forming an insulating film on oneface side of a semiconductor substrate; a second step of forming anelectrode forming groove in an electrode forming region on theinsulating film; a third step of printing an electrode printing pasteincluding metal particles as a main component to a width that covers theelectrode forming groove and a region sandwiching the electrode forminggroove on the insulating film and that is wider than a width of theelectrode forming groove, and then drying the electrode printing paste;and a fourth step of forming an electrode with the width of theelectrode forming groove by firing the electrode paste at a temperaturethat is equal to or higher than a melting point of the metal particlesor that is equal to or higher than a eutectic temperature, andaccumulating and solidifying the electrode paste on the electrodeforming groove.

Advantageous Effects of Invention

According to the present invention, solar battery cells can beinexpensively mass produced that have a finer and thicker electrodewithout increasing the electrode resistance, a suppressed reduction insurface area due to the electrode, and excellent photoelectricconversion efficiency and durability, by using a conventional printingmethod which is low-cost and allows easy mass production.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1-1 is a cross-sectional view illustrating a main part of thecross-sectional structure of a solar battery cell according to anembodiment of the present invention.

FIG. 1-2 is a top view of a solar battery cell as viewed from alight-receiving face side of the solar battery cell according to anembodiment of the present invention.

FIG. 1-3 is a bottom view of a solar battery cell as viewed from theopposite side (back side) of the light-receiving face of the solarbattery cell according to an embodiment of the present invention.

FIG. 2-1 is a cross-sectional view illustrating the production steps ofa solar battery cell according to an embodiment of the presentinvention.

FIG. 2-2 is a cross-sectional view illustrating the production steps ofa solar battery cell according to an embodiment of the presentinvention.

FIG. 2-3 is a cross-sectional view illustrating the production steps ofa solar battery cell according to an embodiment of the presentinvention.

FIG. 2-4 is a cross-sectional view illustrating the production steps ofa solar battery cell according to an embodiment of the presentinvention.

FIG. 2-5 is a cross-sectional view illustrating the production steps ofa solar battery cell according to an embodiment of the presentinvention.

FIG. 3 is a characteristic diagram illustrating the actual printingwidth and actual printing thickness of a post-firing grid electrode withrespect to the design width when a grid electrode is formed by aconventional electrode formation method using a screen printing method.

REFERENCE SIGNS LIST

-   -   1 semiconductor substrate    -   2 p-type silicon substrate    -   3 impurity diffusion layer (n-type impurity diffusion layer)    -   4 anti-reflection film    -   5 light-receiving face side electrode    -   6 front grid electrode    -   7 front bus electrode    -   8 insulating film    -   9 back side electrode    -   10 back grid electrode    -   11 back bus electrode    -   13 front grid electrode forming groove    -   14 back grid electrode forming groove    -   21 front electrode printing paste    -   22 void among metal particles    -   23 back electrode printing paste    -   24 void among metal particles    -   WF front grid electrode width    -   WR back grid electrode width    -   DF front grid electrode thickness    -   DR back grid electrode thickness    -   WF1 front grid electrode forming groove width    -   WR1 back grid electrode forming groove width    -   WF′ printing paste width of front grid electrode    -   WR′ printing paste width of back grid electrode    -   DF′ printing paste thickness of front grid electrode    -   DR′ printing paste thickness of back grid electrode

DESCRIPTION OF EMBODIMENTS

The solar battery cell and production method thereof according to thepresent invention will now be described in more detail based on thedrawings. However, the present invention is not limited to the followingdescription. The present invention may be appropriately changed withinthe scope of what is described herein. Further, for ease ofunderstanding, the scale of the various parts in the drawings may bedifferent from the actual case. In addition, the scale may also varyamong the drawings.

Embodiments

FIGS. 1-1 to 1-3 illustrate a configuration of a solar battery cellaccording to the present embodiment. FIG. 1-1 is a cross-sectional viewillustrating a main part of the cross-sectional structure of the solarbattery cell. FIG. 1-2 is a top view of the solar battery cell as viewedfrom a light-receiving face side. FIG. 1-3 is a bottom view of the solarbattery cell as viewed from the opposite side (back side) of thelight-receiving face. FIG. 1-1 is a cross-sectional view of the mainpart along the line A-A in FIG. 1-2.

As illustrated in FIGS. 1-1 to 1-3, the solar battery cell according tothe present embodiment includes a semiconductor substrate 1 serving as asolar battery substrate that has a photoelectric conversion function andhas a p-n junction; an anti-reflection film 4 formed from a siliconoxide nitride hydride film (SiONH film), which is an insulating filmformed on the light-receiving face (front face) of the semiconductorsubstrate 1 for preventing the reflection of incident light on thelight-receiving face; a light-receiving face side electrode 5 serving asa first electrode that is formed on the light-receiving face (frontface) of the semiconductor substrate 1 and is surrounded by theanti-reflection film 4; an insulating film 8 formed from a silicon oxidenitride hydride film (SiONH film) formed on the face (back face) on theopposite side of the light-receiving face of the semiconductor substrate1; and a back side electrode 9 serving as a second electrode that isformed on the back of the semiconductor substrate 1 and is surrounded bythe anti-reflection film 8, the back side electrode 9 being provided toextract the electricity generated by the semiconductor substrate 1 andreflect incident light.

The p-n junction in the semiconductor substrate 1 is configured from ap-type silicon substrate 2, which is a first conductive layer, and animpurity diffusion layer (n-type impurity diffusion layer) 3, which is asecond conductive layer formed by phosphorous diffusion on thelight-receiving face side of the semiconductor substrate 1. The n-typeimpurity diffusion layer 3 has a surface sheet resistance of 30 to100Ω/.

The anti-reflection film 4 and the insulating film 8 use a silicon oxidenitride hydride film (SiONH film) as a silicon-based insulating filmthat has a comparatively high melting point and does not melt at thefiring temperature during electrode formation. Other than a siliconoxide nitride hydride film (SiONH film), a silicon-based insulation filmsuch as an SiN film may also be used.

The light-receiving face side electrode 5 includes a front gridelectrode 6 and a front bus electrode 7 of the solar battery cell.Further, the light-receiving face side electrode 5 is electricallyconnected to the n-type impurity diffusion layer 3. The front gridelectrode 6 is locally provided on the light-receiving face to collectthe electricity generated by the semiconductor substrate 1. The frontbus electrode 7 is provided roughly orthogonal to the front gridelectrode 6 in order to extract the electricity collected by the frontgrid electrode 6. The dimensions of the front grid electrode 6 are afront grid electrode width WF of 50 μm and a front grid electrodethickness DF of 50 μm. The aspect ratio between the front grid electrodewidth WF and the front grid electrode thickness DF (electrodethickness/electrode width) is 1.

The back side electrode 9 is formed in a comb shape that isapproximately the same as the electrode pattern of the light-receivingface side electrode 5. The back side electrode 9 has a back gridelectrode 10 and a back bus electrode 11. The dimensions of the backgrid electrode 10 are a back grid electrode width WR of 500 μm and aback grid electrode thickness DR of 50 μm. The aspect ratio between theback grid electrode width WF and the back grid electrode thickness DF(electrode thickness/electrode width) is 0.1.

A p+ layer (BSF: back surface filed layer) 12, which is the sameconductive high-concentration diffusion layer as the p-type siliconsubstrate 2, is formed in a region connected to the back side electrode9, which is a region on the back side of the semiconductor substrate 1.

In such a configured solar battery cell, when sunlight is irradiatedfrom the light-receiving face side of the solar battery cell on the p-njunction face (the junction face between the p-type silicon substrate 2and the n-type impurity diffusion layer 3) of the semiconductorsubstrate 1, holes and electrons are generated. Due to the electricalfield of the p-n junction portion, the generated electrons move towardthe n-type impurity diffusion layer 3 and the holes move toward thep-type silicon substrate 2. Consequently, there are too many electronsin the n-type impurity diffusion layer 3 and too many holes in thep-type silicon substrate 2, which results in photovoltaic power beinggenerated. This photovoltaic power is produced in a direction thatbiases the p-n junction in the forward direction. As a result, thelight-receiving face side electrode 5 connected to the n-type impuritydiffusion layer 3 becomes a minus electrode and the back side electrode9 connected to the p-type silicon substrate 2 becomes a plus electrode,so that a current flows in a not-illustrated external circuit.

In the thus-configured solar battery cell according to the presentembodiment, the front grid electrode 6 of the light-receiving face sideelectrode 5 can have a cross-sectional area of about 2,500 μm² and anaspect ratio of 1, so that a fine electrode is realized. Consequently,while maintaining the electrode cross-sectional area and a low electroderesistance, a reduction in the surface area due to the front gridelectrode 6, which is a factor in reducing the effective light-receivingsurface area, can be suppressed, and the photoelectric conversionefficiency can be improved.

Further, in the solar battery cell according to the present embodiment,there are no voids inside the light-receiving face side electrode 5 orthe back side electrode 9. Consequently, in this solar battery cell, itis difficult for moisture or the like, which causes the life of thesolar battery cell to deteriorate, to penetrate into the electrode. Inaddition, an increase in electrode resistance due to voids in anelectrode is prevented.

Therefore, with the solar battery cell according to the presentembodiment, a solar battery cell is realized that has an increasedphotoelectric conversion efficiency and improved durability.

Next, an example of a method for producing this solar battery cell willbe described with reference to FIGS. 2-1 to 2-5. FIGS. 2-1 to 2-5 arecross-sectional views illustrating the production steps of a solarbattery cell according to the present embodiment.

First, as illustrated in FIG. 2-1, for example, a p-type polycrystallinesilicon substrate is prepared as the semiconductor substrate 1(hereinafter referred to as “p-type polycrystalline silicon substrate1”). The p-type polycrystalline silicon substrate 1 is a polycrystallinesilicon substrate that contains a Group III element such as boron (B),and has an electrical resistance of about 0.5 to 3 Ωcm². Since thep-type polycrystalline silicon substrate 1 is produced by slicing aningot formed by cooling and solidifying molten silicon with a wire saw,it still has damage on its surface incurred during the slicing.Therefore, first, to remove this damaged layer, the surface of thep-type polycrystalline silicon substrate 1 is etched by dipping thep-type polycrystalline silicon substrate 1 in a heated alkali solution,such as an aqueous sodium hydroxide solution, whereby damaged regionsnear the surface of the p-type polycrystalline silicon substrate 1 thatwere produced when the silicon substrate was cut are removed.

Next, the p-type polycrystalline silicon substrate 1 is heated for about10 minutes at 820° C., for example, in a phosphorous oxychloride (POCl₃)gas atmosphere, to form an n-type impurity diffusion layer 3 having asurface sheet resistance of 30 to 100 Ω/on the surface of the p-typepolycrystalline silicon substrate 1 as illustrated in FIG. 2-1, wherebya semiconductor p-n junction is formed.

Next, as illustrated in FIG. 2-2, as the anti-reflection film 4 on thesurface of the p-type polycrystalline silicon substrate 1, a siliconoxide nitride hydride film (SiONH film) having a refractive index of 2.0to 2.3 and a thickness of 650 to 900 nm is deposited at a uniformthickness by a PECVD method using oxygen gas (O₂), monosilane gas (SiH₄)and ammonia gas (NH₃). This anti-reflection film 4 also functions as apassivation film on the surface of the p-type polycrystalline siliconsubstrate 1. Further, as illustrated in FIG. 2-2, to improve the crystalproperties of the back side of the p-type polycrystalline siliconsubstrate 1, as the insulating film 8 on the back of the p-typepolycrystalline silicon substrate 1, a similar silicon oxide nitridehydride film (SiONH film) to the anti-reflection film 4 is deposited ata uniform thickness by a PECVD method using oxygen gas (O₂), monosilanegas (SiH₄) and ammonia gas (NH₃).

Next, as illustrated in FIG. 2-3, grooves and holes having a fine widthof 70 μm or less, for example, are formed by laser processing in theregion on the anti-reflection film 4 where the light-receiving face sideelectrode 5 is to be formed. In the present embodiment, as the frontgrid electrode forming groove for forming the front grid electrode 6among the light-receiving face side electrode forming grooves, a frontgrid electrode forming groove 13 having a front grid electrode forminggroove width WF1 of 50 μm is formed using laser light with a wavelengthof 355 nm and a laser energy density of 3 to 10 mJ/cm² in the region onthe anti-reflection film 4 where the front grid electrode 6 is to beformed.

Further, as illustrated in FIG. 2-3, grooves and holes having a finewidth are formed by laser processing in the region on the insulatingfilm 8 where the back side electrode 9 is to be formed. In the presentembodiment, as the back grid electrode forming groove for forming theback grid electrode 10 among the back grid electrode forming grooves, aback side electrode forming groove 14 having a back grid electrodeforming groove width WR1 of 500 μm is formed using laser light with awavelength of 355 nm and a laser energy density of 3 to 10 mJ/cm² in theregion on the insulating film 8 where the back grid electrode 10 is tobe formed.

Next, on the anti-reflection film 4 that includes the light-receivingface side electrode forming grooves as illustrated in FIG. 2-4, thefront grid electrode 6 and the front bus electrode 7 (pre-firing) areformed by screen printing a front electrode printing paste 21 in apattern of the light-receiving face side electrode 5, specifically, inthe patterns of the front grid electrode 6 and front bus electrode 7,and then drying the front electrode printing paste 21. Here, in theregion where the front grid electrode 6 is to be formed, the frontelectrode printing paste 21 is printed to a width that covers the frontgrid electrode forming groove 13 and a region sandwiching this groove onthe anti-reflection film 4, and that is wider than the width of thefront grid electrode forming groove 13, so that a printing paste widthWF′ of the front grid electrode is 100 μm or more and is wider than awidth WF1 of the front grid electrode forming groove. In the presentembodiment, the front grid electrode printing paste 21 is screen printedso that the front grid electrode printing paste width WF′ is 100 μm.

Next, on the insulating film 8 that includes the back side electrodeforming grooves as illustrated in FIG. 2-4, the back grid electrode 10and back bus electrode 11 (pre-firing) are formed by screen printing aback electrode printing paste 23 in a pattern of the back side electrode9, specifically, in the patterns of the back grid electrode 10 and backbus electrode 11, and then drying the back electrode printing paste 23.Here, in the region where the back grid electrode 10 is to be formed,the back electrode printing paste 23 is printed to a width that coversthe back grid electrode forming groove 14 and a region sandwiching thisgroove on the insulating film 8, and that is wider than the width of theback grid electrode forming groove 14, so that a printing paste widthWR′ of the back grid electrode is 500 μm or more and is wider than awidth WR1 of the back grid electrode forming groove. In the presentembodiment, the back grid electrode printing paste 23 is screen printedso that the back grid electrode printing paste width WR′ is 900 μm.

The components of the paste used in the electrode printing will now bedescribed. The front electrode printing paste 21 for the front gridelectrode 6 includes, for example, an ethyl cellulose or thinner solventfor ensuring the printing properties, metal particles of one or aplurality of components selected from silver (Ag), copper (Cu), gold(Au), platinum (Pt), lead (Pd), and aluminum (Al), or an alloy of thesecomponents, and one or a plurality of components selected from zincoxide (ZnO), lead oxide (PbO), silicon monooxide (SiO), and bismuthoxide (BiO), which is a glass component having a lower melting pointthan silver (Ag) used as a reaction promoter during the firing of thep-type polycrystalline silicon substrate 1 with the metal particles. Theabove-described metals can be inexpensively obtained, and are highlyreliable as electrode components for solar battery cells.

For example, for a printing paste that includes 80 wt % of silver (Ag,melting point of 962° C.) as a main component of the printing paste and0.1 wt % of lead monooxide (PbO), a metal and silicon reaction layer canbe obtained at a depth of 0.01 to 0.1 μm at the interface between then-type impurity diffusion layer 3 and the light-receiving face sideelectrode 5 by heating with an infrared heater for 3 seconds at 1,000°C., so that a sufficiently low contact resistance between thelight-receiving face side electrode 5 and the n-type impurity diffusionlayer 3 can be obtained.

Similar to the front grid electrode 6, for the back side electrode 9too, a sufficiently low contact resistance between the back sideelectrode 9 and the p-type silicon substrate 2 can be obtained by usinga printing paste that includes 70 wt % of aluminum (Al) particles as amain component of the printing paste. In addition, since a p+ layer (BSFlayer) 12 more highly doped than the p-type polycrystalline siliconsubstrate 1 can be formed, the recombination rate of the photogeneratedcarriers can be suppressed by a BSF effect, and the solar battery cellconversion efficiency can be increased.

Next, the p-type polycrystalline silicon substrate 1 is fired at atemperature that is equal to or higher than the melting point of themetal particles, which are the main component of the front electrodeprinting paste 21 and the back electrode printing paste 23, or that isequal to or higher than the eutectic temperature. When a plurality oftypes of metal particles are included, the highest melting point oreutectic temperature is used as a standard. The anti-reflection film 4,which is an insulating film, and the insulating film 8 do not have goodwettability with the molten metal. Therefore, the front electrodeprinting paste 21 and back electrode printing paste 23 in which themetal particles are melted accumulate toward the light-receiving faceside electrode forming groove or the back side electrode forming groovewhere the insulating film 8 is not present, without remaining on theanti-reflection film 4 or the insulating film 8, and then solidify.Further, since a silicon oxide nitride hydride film (SiONH film), whichis a silicon insulating film having a comparatively high melting point,is used so that the film does not melt at the firing temperature duringelectrode formation, the anti-reflection film 4 and the insulating film8 do not melt during firing.

During the solidification of the metal, which is the main component ofthe front electrode printing paste 21 and the back electrode printingpaste 23, the printing paste width WF′ of the front grid electrode andthe printing paste width WR′ of the back grid electrode contract to theelectrode width WF and the electrode width WR, respectively. On theother hand, the printing paste thickness DF′ of the front grid electrodeand the printing paste thickness DR′ of the back grid electrode increaseto the electrode thickness DF and the electrode thickness DR,respectively. This happens because of the poor wettability between theinsulating film and the molten metal, so that the front electrodeprinting paste 21 and the back electrode printing paste 23 in which themetal particles have melted accumulate on the light-receiving face sideelectrode forming groove or back side electrode forming groove wherethere is no insulating film 8. Consequently, although the accumulatedmolten metal solidifies at a width that is narrower than the printedwidth, the cross-sectional area of the electrode is nearly maintained.

Then, the front grid electrode 6 (post-firing) is formed in a state inwhich the cross-sectional area has nearly been maintained from when thefront electrode printing paste 21 was printed. As illustrated in FIG.2-5, the front grid electrode 6 (post-firing) is obtained having thesame electrode width as the width WF1 of the front grid electrodeforming groove, with a greater fineness and thickness. Similarly, theback grid electrode 10 (post-firing) is formed in a state in which thecross-sectional area has nearly been maintained from when the backelectrode printing paste 23 was printed. As illustrated in FIG. 2-5, theback grid electrode 10 (post-firing) is obtained having the sameelectrode width as the width WR1 of the back grid electrode forminggroove, with a greater fineness and thickness.

As specific dimensions, for example, if the front grid electrode forminggroove width WF1 is 50 μm, the front grid electrode printing paste widthWF′ is 120 μm, and the front grid electrode printing paste thickness DF′is 25 μm, after the firing a front grid electrode 6 is obtained that hasan electrode width WF of 50 μm, an electrode thickness DF of 50 μm, andan aspect ratio (electrode thickness/electrode width) of 1. Further, ifthe back grid electrode forming groove width WR1 is 500 μm, the backgrid electrode printing paste width WR′ is 900 μm, and the back gridelectrode printing paste thickness DR′ is 30 μm, after the firing a backgrid electrode 10 is obtained that has an electrode width WR of 500 μm,an electrode thickness DR of 50 μm, and an aspect ratio (electrodethickness/electrode width) of 0.1.

The printed and dried front electrode printing paste 21 includes a largeamount of voids 22 among the metal particles due to the mesh of the maskthat is used in the screen printing. Similarly, the printed and driedback electrode printing paste 23 includes a large amount of voids 24among the metal particles due to the mesh of the mask that is used inthe screen printing. However, if the melt time of the metal in theprinting paste is sufficiently long, the voids among the metal particlesthat were present after the printing and drying disappear. Morespecifically, if the firing is carried out for a sufficient time at atemperature equal to or higher than the melting point of the metal,which is the main component of the front electrode printing paste 21 andthe back electrode printing paste 23, or that is equal to or higher thanthe eutectic temperature, the voids 22 and 24 among the metal particlesdisappear, so that a void-free light-receiving face side electrode 5 andback side electrode 9 are obtained. Since moisture and the like whichcause the life of a solar battery cell to deteriorate does not easilypenetrate into electrodes that do not have any voids, the moistureresistance of the solar battery cell is greatly improved, and the lifeof the solar battery cell can be made much longer. Further, the increasein electrode resistance due to voids in the electrode can be prevented,so that a low-resistance electrode can be realized.

As described above, a glass component formed from an oxide of zinc (Zn),lead (Pb), silicon (Si), bismuth (Bi) or the like is included in theprinting paste to obtain an effect that lowers the contact resistancebetween the metal and the silicon substrate. However, the insulatingfilm formed from silicon (Si), nitrogen (N), oxygen (O), hydrogen (H)and the like can melt in the glass component, thereby destroying thestructure of the light-receiving face side electrode forming groove orback side electrode forming groove. Consequently, it is preferred thatthe content of these glass components in the printing paste be as smallas possible. In the present embodiment, since the printing paste issintered by increasing the temperature to or higher than the meltingpoint of the metal particles or to or higher than the eutectictemperature, a sufficiently low contact resistance can be obtained dueto the formation of a reaction layer between the metal and silicon atthe interface between the silicon in the p-type polycrystalline siliconsubstrate 1 and the metal particles, even if the content of these glasscomponents is very small or none.

FIG. 3 is a characteristic diagram illustrating the actual printingwidth (μm) and thickness (μm) of a post-firing grid electrode withrespect to the design width when a grid electrode is formed by aconventional method for forming electrodes using a screen printingmethod. Here, the thickness of the screen printing mask is fixed. As canbe seen from FIG. 3, if the design width is 100 μm, the actual printingwidth of the grid electrode is 120 μm, the actual printing thickness is25 μm, and the aspect ratio (electrode thickness/electrode width) is0.2. Further, it can also be seen from FIG. 3 that the actual printingwidth becomes thicker in proportion to the design width. On the otherhand, even if the design width is less than 100 μm, the actual printingwidth dramatically decreases due to it being more difficult to push theprinting paste out from the screen printing mask as a result of theviscosity of the printing paste. Further, the actual printing widthtends not to change much even if the design width is more than 100μ.Therefore, it is difficult to form a grid electrode having a desiredaspect ratio by a conventional method for forming electrodes using ascreen printing method. It is especially difficult to form a gridelectrode having a high aspect ratio. In the example illustrated in FIG.3, when the design width is set to a value other than 100 μm, it wasdifficult to form a grid electrode having an aspect ratio higher than0.2.

In contrast, with the solar battery cell production method according tothe present embodiment described above, a front grid electrode 6 can beformed that has a post-firing electrode width WF of 50 μm, electrodethickness DF of 50 μm, and aspect ratio (electrode thickness/electrodewidth) of 1, so that a grid electrode having a high aspect ratio can beformed when the design width is set to a value other than 100 μm.

As described above, according to the solar battery cell productionmethod according to the present embodiment, a finer, thicker front gridelectrode 6 can be formed in which the electrode width is narrower andthe electrode is thicker than when the printing paste was printed.Consequently, while maintaining the electrode cross-sectional area and alow electrode resistance, a reduction in the surface area, which is afactor in reducing the effective light-receiving surface area, can besuppressed, and the photoelectric conversion efficiency can be improved.

Further, according to the solar battery cell production method accordingto the present embodiment, there are no voids inside the electrode.Consequently, it is difficult for moisture or the like, which causes thelife of the solar battery cell to deteriorate, to penetrate into theelectrode. In addition, an increase in electrode resistance due to voidsin the electrode is prevented.

Further, since the width of a grid electrode formed by conventionalprinting technology is 100 μm or more, the loss in the light-receivingsurface area of a solar battery cell that is unable to generate powerdue to blockage by the grid electrode is 3% or more. However, with thesolar battery cell production method according to the presentembodiment, since a low-resistance grid electrode can be formed having agrid electrode width of 50 μm or less and an aspect ratio of 0.8 ormore, the photoelectric conversion efficiency of the solar battery cellcan be relatively improved by 2% or more.

Therefore, with the solar battery cell production method according tothe present embodiment, solar battery cells having greater photoelectricconversion efficiency and improved durability can be mass producedinexpensively.

The invention claimed is:
 1. A method for producing a solar batterycell, characterized by comprising: a first step of forming an insulatingfilm on one face side of a semiconductor substrate; a second step offorming a groove in the insulating film for forming an electrode formingregion; a third step of printing an electrode printing paste includingmetal particles as a main component to a width that covers the electrodeforming region groove and a region sandwiching the electrode formingregion groove in the insulating film and that is wider than a width ofthe electrode forming region groove, and then drying the electrodeprinting paste; and a fourth step of forming an electrode with the widthof the electrode forming region groove by firing the electrode paste ata temperature that is equal to or higher than a melting point of themetal particles or that is equal to or higher than a eutectictemperature, and accumulating and solidifying the electrode paste on theelectrode forming region groove.
 2. The method for producing the solarbattery cell according to claim 1, wherein there are no voids in theelectrode.
 3. The method for producing the solar battery cell accordingto claim 1, wherein the semiconductor substrate is a silicon substrate,and the electrode printing paste includes metal particles of one or aplurality of components selected from silver, copper, gold, platinum,lead, and aluminum, or an alloy of these components.
 4. The method forproducing the solar battery cell according to claim 1, wherein theinsulating film is a silicon insulating film.
 5. The method forproducing the solar battery cell according to claim 1, wherein theelectrode is a light-receiving face side electrode, and the insulatingfilm is an anti-reflection film.